{"schemaVersion":1,"slug":"wound-primary-current-transformer","name":"Wound-primary current transformer","kind":"symbol","abbreviation":"CT","aliases":["wound CT","wound-type current transformer"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"CT with a primary winding of several turns, used for low primary currents where a bar primary gives too little accuracy.","description":["A wound-primary CT has a primary winding of more than one turn rather than a single bar or conductor through a window. This is needed at low primary currents, where a single turn would not produce enough magnetising ampere-turns for accurate metering, and it is common in MV metering units.","The wound primary has a lower short-time withstand than a bar primary, so its thermal and dynamic ratings need checking against the fault level. The symbol shows the winding but not those ratings, which belong in the CT schedule."],"readingNotes":["Check the short-time thermal rating against the fault level.","Read primary terminals P1 and P2 for polarity."],"drawingChecklist":["State ratio and class","Give short-time rating","Show polarity marks"],"distinction":"A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary.","facts":[{"label":"Primary","value":"Multi-turn winding"},{"label":"Typical use","value":"Low primary currents and metering units"},{"label":"Preview","value":"Independent educational concept; consult the applicable standard and project legend for the exact graphic"}],"references":[{"sourceId":"instrument-transformers","relevance":"Public manufacturer overview of indoor current and voltage instrument transformers."},{"sourceId":"autodesk-ct","relevance":"Public AutoCAD Electrical current transformer family used for context; this variant is independently drawn."}],"related":["current-transformer","ansi-current-transformer-with-primary-conductor-indication","combined-instrument-transformer"],"artwork":"s28-wound-primary-current-transformer","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","plainEnglish":{"title":"What does Wound-primary current transformer mean?","introduction":"A wound-primary CT has a primary winding of more than one turn rather than a single bar or conductor through a window. This is needed at low primary currents, where a single turn would not produce enough magnetising ampere-turns for accurate metering, and it is common in MV metering units.","example":"The wound primary has a lower short-time withstand than a bar primary, so its thermal and dynamic ratings need checking against the fault level. The symbol shows the winding but not those ratings, which belong in the CT schedule.","drawings":"Check the short-time thermal rating against the fault level. Read primary terminals P1 and P2 for polarity. A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary.","terms":[{"name":"Winding","meaning":"A coil of conductor inside an electrical machine or transformer."},{"name":"Rating","meaning":"A value stating the conditions for which equipment is specified."},{"name":"Schematic","meaning":"A drawing showing function and connections rather than physical appearance."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"Indoor current and voltage transformers","url":"https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers"},{"label":"Current transformer symbol variants","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-40AAEF4A-AC3F-4B3D-90A5-A9E0707C1241.htm"}],"detail":"CT with a primary winding of several turns, used for low primary currents where a bar primary gives too little accuracy. A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/wound-primary-current-transformer","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/wound-primary-current-transformer.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"instrument-transformers","title":"Indoor current and voltage transformers","publisher":"ABB","url":"https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers","type":"manufacturer","scope":"Public current- and voltage-transformer product families. Ratings, terminals and dimensions depend on the model.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public manufacturer overview of indoor current and voltage instrument transformers."},{"id":"autodesk-ct","title":"Current transformer symbol variants","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-40AAEF4A-AC3F-4B3D-90A5-A9E0707C1241.htm","type":"cad-reference","scope":"Current transformers, secondaries and conductor indications; vendor block identifiers are distinct from IEC symbol identifiers.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public AutoCAD Electrical current transformer family used for context; this variant is independently drawn."}]}